Lordotic spinal implant

ABSTRACT

A lordotic implant has a frusto-conical shape with external threads. Prior to placement of the implant, vertebrae are distracted in a manner to provide a desired lordosis between the vertebrae. The pre-distracted vertebrae are then tapped to provide a tapped bore having a geometry matching the conical geometry of the implant. The threaded implant is then placed within the pre-tapped conical bore.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part application of U.S.Ser. No. 08/812,791, filed Mar. 6, 1997, (now abandoned) the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention pertains to spinal implants and surgical procedures foruse in spinal stabilization. More particularly, this invention pertainsto an apparatus and method for implanting a tapered implant between twovertebrae.

2. Description of the Prior Art

Chronic back problems can cause pain and disability for a large segmentof the population. In many cases, the chronic back problems areattributed to relative movement between vertebrae in the spine.

Orthopedic surgery includes procedures to stabilize vertebrae. Commonstabilization techniques include fusing the vertebrae together. Fusiontechniques include removing disk material which separates the vertebraeand impacting bone into the disk area. The impacted bone fuses with thebone material in the vertebrae to thereby fuse the two vertebraetogether.

To increase the probability of a successful fusion, spinal implants havebeen developed. Commonly assigned U.S. Pat. No. 5,489,307 discloses ahollow threaded cylindrical implant. That patent also discloses a methodof placing the implant between two vertebrae.

The method of U.S. Pat. No. 5,489,307 discloses parallel distraction ofopposing vertebrae prior to placing an implant. However, not allvertebrae are in parallel opposition. A normal and healthy spine has anatural curvature referred to as lordosis. As a result of the curvature,opposing vertebrae are positioned with their end plates in non-parallelalignment depending upon the position in the spine. For example, in thelumbar region of the spine, the end plates of the L-4 and L-5 vertebraemay be at an angle of about 3°-15°. Similarly, the opposing end platesof the L-5 and S-1 vertebrae may be at about 8°-16° lordosis. The actualamount of lordosis varies with the location of the spine and varies frompatient to patient. It is desirable to provide an implant whichmaintains or achieves a desired lordosis between opposing vertebrae anda method of placing the implant.

SUMMARY OF THE INVENTION

According to one embodiment of the present innovation, a spinal implantis disclosed having a taper from a leading end to a trailing end equalto a desired lordosis.

In an alternative embodiment, a spinal implant can have two tapers.According to this embodiment the implant has a first taper divergingaway from the axis of the implant from the leading end to a terminalend. A second taper diverges away from the axis of the implant from theterminal end to the leading end. The tapers meet at the "trailing endrise". The "trailing end rise" (TRE) and the terminal end arecollectively referred to as the trailing end. In a preferred embodimentthe implant has a terminal end and a leading end which are ofsubstantially equal diameters.

The method of the invention includes placing a tapered distraction pluginto the disk space between the vertebrae on one side of the vertebrae.On the opposite side of the vertebrae, a tapered tap is used to tap athread pattern into the opposing vertebrae. The implant is placed intothe tapped space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a right side elevation view of a lordotic implant according tothe present invention (the opposite side being identical in appearance);

FIG. 2 is an elevation view of a trailing end of the implant of FIG. 1;

FIG. 3 is an end elevation of a leading end of the implant of FIG. 1;

FIG. 4 is a top plan view of the implant of FIG. 1 taken 90° from theview of FIG. 1 (the opposite side being identical in appearance);

FIG. 5 is a view taken along line 5--5 of FIG. 4;

FIG. 6 is an enlarged cross-sectional view of thread detail of theimplant of FIG. 1;

FIG. 7 is a side elevation view of a distraction plug for use in thepresent invention;

FIG. 7A is a side elevation view of a tool for placing the plug of FIG.7;

FIG. 8 is a side elevation view of a pre-boring tool for use in thesurgical method of the present invention;

FIG. 9 is an elevation view of a distal end of the tool of FIG. 8;

FIG. 10 is a side elevation view of guide pin for use with thepre-boring tool of FIG. 8;

FIG. 11 is a side elevation view of a tap according to the presentinvention;

FIG. 12 is a view taken along line 12--12 of FIG. 11;

FIG. 13 is a cross-sectional view of threads of the tap of FIG. 11;

FIG. 14 is a side elevation view of a driver for use in the method ofthe present invention;

FIG. 15 is a top plan view of the driver of FIG. 14;

FIG. 15A is a side elevation view of a tool for holding the implant ofFIG. 1 in the driver of FIG. 15;

FIG. 15B is a side elevation view of a tool for releasing the implant ofFIG. 1 from the driver of FIG. 15;

FIG. 16 is an elevation view of a distal end of the driver of FIG. 14;

FIG. 17 is an enlarged cross-sectional view of a thread pattern on thedriver of FIG. 14;

FIG. 18 is a schematic side elevation view of vertebrae in the spine;

FIG. 19 is a side elevation schematic view of opposing L-5 and S-1vertebrae prior to the method of the present invention;

FIG. 20 is the view of FIG. 19 following placement of the distractionplug of FIG. 7;

FIG. 21 is the view of FIG. 20 showing boring with the tool of FIG. 10;

FIG. 22 is the view of FIG. 21 showing tapping with the tool of FIG. 11;

FIG. 23 is the view of FIG. 22 showing placement of the implant of FIG.1;

FIG. 24 is an anterior to posterior view of FIG. 23;

FIG. 25 is a right side elevation view of an embodiment for a lordoticimplant according to the present invention illustrating a first andsecond taper (the opposite side being identical in appearance);

FIG. 26 is a top plan view of the implant of FIG. 25 taken 90° from theview of FIG. 25 (the opposite side being identical in appearance);

FIG. 27 is a view taken along line 27--27 of FIG. 26;

FIG. 28 is a right side elevation view of an alternative embodiment of alordotic implant according to the present invention illustrating a firstand second taper (the opposite side being identical);

FIG. 29 is an elevation view of a terminal end of the implant of FIG.25;

FIG. 30 is an elevation view of a leading end of the implant of FIG. 25;

FIG. 31 is a side elevation of an embodiment of a distraction plug ofthe invention (the opposite side being identical in appearance);

FIG. 32 is a side elevation of the distraction plug of FIG. 31 rotated90° from the view of FIG. 31 (the opposite side being identical inappearance);

FIG. 33 is a frontal view of the leading end of the distraction plug ofFIGS. 31 and 32.

FIG. 34 is a side elevation of an alternative embodiment of adistraction plug of the invention (the opposite side being identical inappearance);

FIG. 35 is a side elevation of the distraction plug of FIG. 34 rotated90° from the view of FIG. 34 (the opposite side being identical inappearance);

FIG. 36 is a frontal view of the leading end of the distraction plug ofFIGS. 34 and 35; and

FIG. 37 is a top view of a T-device for removal of a distraction plugfrom a tool.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference now to the various drawing Figures in which identicalelements are numbered identically throughout, a description of thepreferred embodiment under the present invention will now be provided.As will become apparent, the present invention utilizes certain surgicalmethods and tools disclosed more fully in U.S. Pat. No. 5,489,307incorporated herein by reference.

With initial reference to FIG. 18, a healthy spine is schematicallyshown to illustrate lordosis in the spine. As shown in the example ofFIG. 18, the end plates 10₂, 10₃ of vertebrae L-2 and L-3 are inparallel alignment. Similarly, the end plates 10₃ ' and 10₄ of vertebraeL-3 and L-4 are in parallel alignment. However, the end plates 10₄ ' and10₅ of vertebrae L-4 and L-5 are at a 3° angle with the widestseparation on the anterior, A, side of the spine and the narrowestseparation on the posterior, P, side of the spine. Similarly, the endplates 10₅ ' and 10₁ of vertebrae L-5 and S-1 are at an 8° angle (withthe widest separation on the anterior side of the spine). It will beappreciated that the examples given are illustrative only. The actualdegree of lordosis will vary from patient to patient and within theregion of the spine.

Where a physician determines that spinal fusion is desired betweenlordotically separated vertebrae, the present invention is directed toan apparatus and method for fusing the opposing vertebrae whilemaintaining lordosis. Further, where an attending physician determinesthat fusion is desirable and further determines that increased lordosisis desirable, the present invention is directed towards an apparatus andmethod for both fusing the spine and for increasing the amount oflordosis between the vertebrae to a degree of separation determined bythe attending physician. The present invention will be described inapplication to the latter example illustrated in FIG. 19 where the endplates 10₅ ' and 10₁ of opposing vertebrae L-5 and S-1 are parallel anda physician determines that an 8° lordosis is desirable in addition toplacing a fusion implant between the vertebrae.

A. IMPLANT.

With initial reference to FIGS. 1-6, an implant 20 according to thepresent invention is shown. The implant 20 has a longitudinal axis X--Xextending from a leading end 22 to a trailing end 24.

The implant 20 has a substantially frusto-conical shape with a conicalangle α equal to a desired lordosis between the vertebrae into which theimplant 20 is to be placed. In the example given, angle α is 8°.However, it will be appreciated that such implants 20 will be availablein a wide variety of sizes. For example, such implants may be providedhaving angles α ranging from 1° to 20° in 1° increments to permit anattending physician to select a desired implant to attain a desiredlordosis. Further, such implants can be provided in varying sizes (i.e.,the diameters of the implants) to accommodate desired distraction andlordosis between opposing vertebrae.

The implant 20 has helical threads 26 surrounding the conical surface ofthe implant 20. Shown best in FIG. 6, the threads 26 are generallysquare in cross-section with their flat outer peripheral surfaces 26aset at an angle of one-half α with respect to the longitudinal axis X--Xand define valleys 28 between the threads 26.

At the leading end 22, the implant has a major diameter D_(M) measuredbetween diametrically opposite outer radial surfaces 26a of the threads26 at the leading end 22. At the leading end 22, the implant 20 has aminor diameter D_(m) measured as the distance across the implant 20between the valleys 28 of the thread pattern 26.

At the trailing end 24, the implant 20 has a major diameter D'_(M)measured between diametrically opposite outer radial surfaces 26a ofthreads 26 at the trailing end 24. Finally, at the trailing end 24, theimplant 20 has a minor diameter D'_(m) measured between diametricallyopposite valleys 28 at the trailing end 24.

For purposes of illustration, representative sizings of the implant 20will have a leading end major diameter D_(M) of about 0.56 inches and aminor diameter D_(m) at the leading end 22 of about 0.46 inches. At thetrailing end 24, the major diameter D'_(M) is about 0.69 inches and theminor diameter D'_(m) is about 0.59 inches. The length L (FIG. 4) of theimplant (measured from the leading end 22 to the trailing end 24) isabout 0.95 inches. Again, it will be appreciated that the foregoingdimensions are illustrative only and the sizing can vary to accommodatea surgeon's selection of a desired sizing for placement into a diskspace.

The implant 20 is hollow to present a hollow implant interior 30. FIG. 4illustrates a top side of the implant 20. As shown, the implant includesaxially aligned holes 32 extending through the conical wall of theimplant into communication with the interior 30. The holes 32 areprovided on diametrically opposite sides of the implant (i.e., the sideof the implant opposite that shown in FIG. 4 is identical to that shownin FIG. 4). The holes 32 therefore extend completely through the implant20 to define a hollow column through which bone may grow from opposingvertebrae after the implant is placed between the vertebrae and with theholes 32 facing the vertebrae.

The holes 32 on a given side (such as that shown in FIG. 4) areseparated by a central reinforcing rib 34. Further, a reinforcing rib 36is provided at the leading end 22 and a reinforcing rib 38 is providedat the trailing end 24 to resist compression forces on the implant 20after it is placed between opposing vertebrae.

The trailing end 24 is provided with an axially positioned threaded bore40, the purposes of which will be described. The leading end 22 isprovided with an oval bore 42 having its major axis aligned with theopposing holes 32. Bone chips or other bone growth inducing substancesmay be placed into the interior of the implant 20 to promote fusionfollowing placement of the implant 20 between opposing vertebrae.

As best illustrated in FIGS. 1-3, the thread pattern 26 is notcontinuous. Instead, the sidewalls of the implant 20 are provided withcutouts 44,44' on the sides of the implant which are 90° offset from thesides containing the holes 32. The cutouts 44, 44' present flatsidewalls 44a, 44a' recessed inwardly from a cone defined by the threads26. The sidewalls have holes 31 therethrough in communication withinterior 30.

As best illustrated in FIGS. 2 and 3, the cutouts 44,44' are at anglesβ,β for purposes that will become apparent. In a representative example,β is 65° and β' is 62°.

B. DISTRACTION SPACER AND INSERTION TOOL.

For use in placing the implant 20 between opposing vertebrae, adistraction spacer 50 is used. The distraction spacer 50 is shown inFIG. 7. The distraction spacer 50 is generally conical and has a mainbody portion 52 with a conical angle α' equal to the angle α of theimplant 20. Accordingly, a kit containing numerous sized angles for animplant 20 may contain numerous sized distraction spacers with α'matching the implants 20.

Leading end 54 is provided with an additional taper to permit ease ofinsertion of the distraction spacer 50 into a disk space. Near thetrailing end 58, the distraction spacer 50 includes an annular groove 60to permit a surgeon to grasp the distraction spacer 50 if needed. Themain body 52 is provided with a knurling 62 such that the distractionspacer 50 resists undesired movement following placement of thedistraction spacer 50 into a disk space. The trailing end 58 is providedwith an internally threaded axial bore 64 for attachment of a placementtool as will be described.

The distraction spacer 50 is sized to have an outer conical surfacesubstantially equal to a conical surface defined by the minor diametersof the implant 20. Namely, at the trailing end 58, the diameter of thedistraction spacer 50 is approximately equal to the trailing end minordiameter D'_(m) of the implant 20. The distraction spacer is symmetricalabout its longitudinal axis X'--X' and has an axial length L'approximate to the length L of the implant and sized for the distractionspacer 50 to be fully inserted into the disk space without protrudingbeyond the vertebrae.

FIG. 7A illustrates a tool 300 for placing plug 50. The tool 300 has ashaft 302 with a handle 304 at a proximal end. A threaded stud 303 isprovided at the distal end. The stud 303 is threadedly received withinbore 64 of plug 50 to axially align the longitudinal axes of the plug 50and shaft 302.

C. BORING TOOL.

FIG. 8 illustrates a pre-boring tool 70 for initial boring of thevertebrae prior to insertion of the implant and prior to tapping for theimplant 20. The pre-boring tool 70 includes a shaft 71 having a taperedcutting head 72 (tapered at angle α) at a distal end of the tool 70.

A proximal end of the shaft 71 is provided with a stop flange 73 forlimiting insertion of the boring tool 70 into a guiding drill tube (notshown). The shaft 71 includes enlarged diameter portions 74 to be inclose tolerance with the internal diameter of a drill tube to ensurethat the tool 70 does not have relative radial movement to a drill tubeas the tool 70 is being axially advanced within a drill tube.

The cutting head 72 is provided with cutting teeth 75 to cut a taperedbore as the tool is rotated about its longitudinal axis X"--X". Theteeth 75 are sized to cut a bore having a leading end diameter equal tothe leading end minor diameter D_(m) of the implant 20 and a trailingend diameter equal to the implant's trailing end minor diameter D_(M).The distal end of the cutting head 72 is provided with an axiallyextended threaded bore 76 to receive a guide pin such as those shown asitem 64 in FIG. 56 of the aforementioned U.S. Pat. No. 5,489,307attached to pre-boring tool 112 in the '307 patent.

Such a guide pin is shown in FIG. 10. The pin 200 has a tapered body 202tapered at angle α with an axially extending stud 203 to be receivedwithin bore 76. A leading end 204 is provided with flutes 206 to removedisk material as the guide pin 200 is advanced. The selected guide pin200 will have a diameter, D₃, equal to about 3 millimeters less than thediameter of a bore being cut by cutting head 72. A leading end diameter,D₄, is equal to the leading end diameter of the distraction spacer 50.

D. TAP.

FIGS. 11-13 illustrate a novel tap 80 for use in the method of thepresent invention. The tap 80 includes a shaft 81 having an axisX'"--X'". A distal end of the shaft 81 is provided with a tapping head82.

A proximal end of the shaft 81 is provided with stop flange 83 forlimiting insertion of the tap 80 into a guiding drill tube (not shown).The shaft 81 includes enlarged diameter portions 84 sized to approximatean internal diameter of a guide tube (not shown) to ensure no relativeradial movement of the tap 80 relative to a drill tube as the tap 80 isbeing axially advanced through a drill tube.

The novel tapping head 82 includes a hollow interior 86 with a closedaxial or distal end 88. A thread pattern 90 surrounds the tapping head82 but is spaced from the axial end 88 by an unthreaded guide tip 92.

Illustrated best in FIG. 13, the threads 90 are V-shaped incross-section and extend from flat valleys 94 to pointed thread tips 96.The valleys 94 define a conical surface having an internal angle α"equal to the angle α of implant 20. Similarly, the tips 96 define aconical surface having an internal conical angle equal to α. The depthof the threads 96 (i.e., the distance between the tips 96 and thevalleys 94) is equal to the depth of the threads 26 (i.e., the distancebetween the surfaces 26a and the valleys 28) of the implant 20.

The guide tip 92 is cylindrical and has a diameter D_(T) equal to theleading end minor diameter D_(m) of implant 20. The starting thread 90'accordingly has a minor diameter of the same size as the minor diameterD_(m) of the starting thread of the implant 20. Also, starting thread90' has a major diameter equal to the leading end major diameter D_(M).The ending thread 90" has a minor diameter equal to the trailing endminor diameter D'_(m) of implant 20. Further, the ending thread 90" hasa major diameter equal to the major diameter D'_(M) of the implant 20.The threading has a length L_(T) equal to the length L of the implant20. Accordingly, the thread pattern 90 is identical in sizing and anglesto the thread pattern 26 of implant 20 except for the cross-sectionprofile with threads 96 being V-shaped and with threads 26 beinggenerally square in cross-section (best illustrated comparing FIGS. 6and 13).

With reference to FIGS. 11 and 12, the thread pattern 96 includes threecutouts 100 to define cutting edges 102 to permit the threads 96 to tapa thread pattern as the cutting head is rotated in a counterclockwisedirection in the view of FIG. 12. Channels 104 are provided from thecutouts 100 and extending into communication with the hollow interior86. The channels 104 define pathways to permit debris formed by thetapping to be accumulated within the interior 86. Further, additionalchannels 106 are provided in the valleys 94 between opposing threads.The channels 106 further extend into communication with the interior 86to provide additional pathways for debris to flow into the interior 86.Accordingly, during tapping with the tool 80, debris formed by thetapping is accumulated within the interior 86. Due to the closed end 88,the debris is retained within the interior 86 when the tap 80 is removedfrom the disk space.

E. IMPLANT DRIVER.

FIGS. 14-17 illustrate a driver 110 for use in placing an implant 20into a prepared space. The driver 110 includes a shaft 112. A distal endof the shaft 112 is provided with a driving head 114. A proximal end ofthe shaft 112 is provided with a handle 117.

The shaft 112 is hollow throughout its length defining an axiallyextending bore 113. The handle 117 includes a large diameter recess 115and a narrower diameter recess 119. Recess 119 is threaded for reasonsthat will become apparent.

The driving head 114 includes axially extending gripping prongs116,116'. The gripping prongs 116,116' are diametrically opposed and arepositioned and shaped to be complementary to the cutouts 44,44',respectively of the implant 20. The side edges 116b' define an angle β*slightly less than angle β while the side edges 116b define an angle β*'slightly less than angle β'. For example, with reference to thedimensions given for β and β' in FIG. 2, the angle β* is about 63° andthe angle β*' would be about 60° to permit minor relative rotationalmovement of the prongs 116,116' within the cutouts 44,44'.

As illustrated best in FIG. 17, the prongs 116,116' include threads 118positioned and shaped to complete the thread pattern 26 of the implant20. Namely, the implant 20 may be placed in the driving head 114 withthe trailing end 24 abutting the end 112a of the shaft 112 and with theleading end 22 flush with the ends 116a, 116a' the prongs 116,116'. As aresult, when the implant 20 is placed within the driving head 114, theprongs 116a, 116a' cover the sidewall openings 31 of the flat sidewalls44a, 44a' of the implant 20 such that the implant 20 together with theprongs 116,116' define a continuous externally threaded frusto-conicalshape and with the threads 26 aligned with the threads 118 to define acontinuous thread pattern.

In FIG. 15A, a tool 800 is shown to hold implant 20 in driver 110. Thetool 800 has a shaft 802, a handle 806 and a threaded end 804. End 804is threaded into the bore 40 of an implant 20 placed between prongs 116,116'. When so positioned, the handle 806 is seated within recess 115 andshaft 802 extends through bore 113 to securely and releasably affiximplant 20 within driver 110.

FIG. 15B shows a tool 900 for separating the implant 20 from the driver110. With tool 800 removed from bore 113, the shaft 906 of tool 900 isplaced in bore 113. The blunt end 904 abuts the trailing end 24 of theimplant 20. A threaded portion 908 engages the threads of bore 119. Byturning handle 902, the blunt end 904 urges the implant 20 out frombetween prongs 116, 116'.

F. SURGICAL METHOD.

Having thus described the novel implant 20, distraction spacer 50 andtools 70, 80, 110, the method of the present invention will now bedescribed.

With reference to FIG. 19, an L-5 and S-1 vertebrae are shown with adiseased disk space 130 between the opposing end plates 10'₅ and 10₁.For ease of illustration, disk material is not shown within the diskspace 130. In the example of FIG. 19, the end plates 10'₅ and 10₁ are inparallel alignment and are to be distracted (i.e., separated) as well asbeing provided with a desired lordosis which in the example is 8°.

As illustrated in FIG. 24 (which is a view from the anterior to theposterior), a sagittal plane S divides the vertebrae into a left side Land a right side R. A preferred surgical approach is an anteriorapproach performed laparoscopically. Procedures such as removal of diskmaterial are not described or illustrated and are known in the art.

A selected distraction spacer 50 (i.e., a distraction spacer sized andprovided with a conical angle selected by the physician to attain adesired distraction and lordosis) is attached to tool 300 with the shaftthreaded into the threaded bore 64. The distraction spacer 50 is forcedinto space 130 on the left side until the distraction spacer 50 is fullyreceived within the disk space such that the end 58 does not protrudeout of the disk space. The tool 300 is then unthreaded from thedistraction spacer 50 and removed through the drill tube leaving thedistraction spacer in place.

With the examples given, the distraction spacer 50 urges the disks L-5and S-1 apart by reason of the conical surface of the distraction spacerurging against the end plates 10'₅ and 10₁. In addition to distractingthe vertebrae L-5 and S-1, the distraction plug 50 induces a desiredlordosis of 8° to the vertebrae L-5 and S-1 as illustrated in FIG. 20.

Leaving the distraction spacer 50 in place, a drill tube (not shown butwhich may be such as that shown in U.S. Pat. No. 5,489,307) is placed onthe right side of the disk space 130. A bore is then formed partiallyinto the opposing vertebrae L-5 and S-1 as illustrated in FIG. 21. Toform the bore, the pre-boring tool 70 with an attached guide pin 200 isfirst inserted into drill tube. The guide point acts against theopposing surfaces of the end plates 10₅ ', 10, to initially centrallyalign the boring tool 70 within the disk space 130.

By rotating the pre-boring tool 70, the cutting head 72 cuts an initialdepth of a bore into the vertebrae L-5, S-1. Due to guide 200, a bore iscut by head 72 only about 50% of the way into the disk space.

It will be appreciated that pre-boring tools such as tool 70 havingguide pins to initially form a bore between opposing vertebrae is notpart of this invention per se and is disclosed and described in U.S.Pat. No. 5,489,307. The '307 patent further discloses forming a finalbore with a final boring tool. Since the vertebrae L-5 and S-1 aredistracted with a lordosis of 8° and the boring tools having cuttingheads which are tapered, a bore is only partially cut into the vertebraeby the pre-boring tool with no bore formation at the posterior ends ofthe vertebrae L-5, S-1. The posterior end will be simultaneously boredand tapped by the debris retaining tap.

After the formation of the desired bore by the boring tool 70, the tap80 is inserted into the drill tube as illustrated in FIG. 22. The minordiameter of the threads of the tap 80 will be substantially equal to thespacing of the end plates such that the V-shaped threads 90 of the taponly cut into the end plates 10₅ ', 10, as illustrated in FIG. 22.

Since the tap 80 is provided with a conical angle substantially equal tothe angled separation of the distracted vertebrae, the tap 80 forms atapped bore between the vertebrae L-5, S-1 with a thread patternmatching the thread pattern of the implant 20. After removal of the tap,debris formed in the tapping process is removed from the disk space 130by reason of the debris being captured within the interior 86 of thetapping head 82.

With the tapping operation complete, the implant 20 is inserted into thedistal end of the driver 110 and retained therein by tool 802. Theimplant 20 is filled with bone or other suitable bone growth inducingsubstance. The driver 110 and attached implant 20 are then insertedthrough the drill tube and threadedly urged into the pre-tapped borebetween the vertebrae L-5 and S-1.

As mentioned, the pre-tapped bore matches the size and thread pattern ofthe implant 20 except only that the pre-tapped threads of the bore areV-shaped and the threads 26 of the implant 20 are square incross-section. By reason of this difference in geometry of the threads,forcing the square cross-section threads 26 of the implant into theV-shaped tapped threads causes material of the vertebrae to becompressed as the implant is inserted into the disk space 130. Thiscompression further increases distraction and securely lodges theimplant 20 within the disk space 130 to prevent undesired movement ofthe implant 20 relative to the vertebrae.

Rotation of the implant and driver within the disk space is continueduntil the implant 20 is fully inserted within the disk space 130 and theprongs 116,116a' are aligned with the disk space 130. With the prongs116, 116a' so aligned, the holes 32 directly oppose the bone of thevertebrae L-5, S-1. The implant 20 and boring and tapping tools 110, 80are sized such that the tapping exposes the cancellous bone of thevertebrae to encourage bone growth from the vertebrae through theimplant and in communication with any bone growth inducing substanceplaced within the interior 30 of the implant. Also, the threads 26 ofthe implant 20 will be opposing and retained within the cortical bone ofthe vertebrae L-5, S-1 to resist subsidence of the implant 20 into thevertebrae.

With the implant finally positioned, the driving tool 110 is removed byaxially pulling on the tool. Due to frictional forces, the driving tool110 may resist removal. In such an event, the removal tool 900 may beinserted within the bore 113 forcing separation of the tool 110 from theimplant 20 to facilitate ease of removal. FIG. 24 illustrates an implant20 inserted between the vertebrae L-5, S-1 on the right side and with adistraction spacer 50 still in place on the left side. After insertionof an implant 20 on a right side, the guide tube may be moved to theleft side. The distraction spacer 50 may then be removed and the leftside may be prepared for implant insertion by boring and tapping asdescribed above and a second implant may be placed in the left side.

DESCRIPTION OF ALTERNATIVE IMPLANT AND DISTRACTION SPACER EMBODIMENTS

A. IMPLANT

Referring to FIGS. 25-30, another embodiment of an implant is shown. Theimplant 400 can be used with the tools and methods described above.According to this embodiment, the implant 400 has a first and secondtaper and a longitudinal axis X--X extending from a leading end 401 to atrailing end 402. The trailing end 402 of the present embodimentcomprises a "trailing end rise" (TER) 403 and a terminal end 404. Thefirst taper of implant 400 diverges from the axis from the leading end401 to the trailing end rise 403 of the trailing end 402. The secondtaper diverges from the axis from the terminal end 404 to the TER 403.The trailing end rise is the region of greatest diameter of the implant400. As described below, the second taper provides implantationadvantages for the surgeon as well as increased safety for the patient.

The bi-tapered implant 400 includes leading end 401 having a first taperproviding a substantially frusto-conical shape with a conical angle αequal to a desired lordosis between selected vertebrae. The angle α ofthe illustrated embodiment, measured from the leading end 401 to the TER403 is 8°, however, as described for other embodiments of the invention,the implants will be available with a variety of angles and sizes.

Referring to FIG. 25, leading end 401 has a major diameter D_(M)measured between diametrically opposite outer radial surfaces 405a ofthe threads 405 at the leading end 401. The leading end 401 also has aminor diameter D_(m) measured between diametrically opposite innerradial surfaces 408a of the valleys 408 of the thread pattern 405 ofimplant 400.

At the trailing end 402, the implant 400 has a major diameter D'_(M)measured between diametrically opposite outer radial surfaces 405b ofthreads 405 at the trailing end rise 403. The trailing end 402 also hasa minor diameter D_(E) measured across terminal end 404.

The second taper of implant 400 has a second angle, δ, extending fromthe terminal end 404 to the TER 403. The angle δ will vary with thediameter D'_(M) of the TER 403, the diameter D_(E) of the terminal end404, and the longitudinal distance L_(E) therebetween. In theillustrated embodiment, the diameter D_(E) of the terminal end 404 isequal to the major diameter D_(M) of the leading end 401.

The longitudinal distance L_(E) can be about 5% to 25% of the overalllength L of the implant. Generally, L_(E) is less than 15% of theoverall length L, typically about 8-10%.

It will be appreciated that the slope "m" of the second taper, relativeto the longitudinal axis X--X, can be calculated by the equation:

    D'.sub.M -D.sub.E /L.sub.E

In the illustrated embodiment, m is about 1 (45°). However, the actualslope dimension m can vary, typically, between 0.58 (30°) and 1.73(60°).

The helical threads 405 can extend along the second taper as illustratedat 406 of FIGS. 25-27. Alternatively, as illustrated in FIG. 28, thethreads 405 can stop at the terminal rise 403 and the second tapercomprise a flat 410, undulating or other non-thread bearing surface,from trailing end rise 403 to terminal end 404. FIGS. 29 and 30illustrate the terminal end and leading end, respectively, of implant400. Other features described for the implant embodiment 20 are alsoapplicable to implant 400.

The second taper of implant 400 provides installation advantages for thesurgeon and enhanced safety features for the patient. For the surgeon,the trailing end taper allows a greater margin of error in the desiredlength of the bore formed for inserting the implant. That is, in somecircumstances, if the length of the bore formed is less than the lengthof the implant, the tapered trailing end 402 permits insertion ofimplant 400 into the "short" bore without leaving a trailing end exposedbeyond the surface of the vertebrae that has a sharp or abrupt edge. Inaddition, once implanted during surgery, the tapered trailing end ofimplant 400 facilitates re-engaging the implant driver to adjust theanterior/posterior position of the implant.

For patient safety, once placed between the end plates of opposingvertebrae, should the implant 400 back out or become displaced, thesecond taper at the trailing end reduces the likelihood that thetrailing end would erode through major blood vessels, the peritoneum orother structures surrounding the implanted device.

B. DISTRACTION SPACER

FIGS. 31-36 illustrate additional embodiments of a distraction spacer("plug") suitable for use with lordotic implants or non-tapered typeimplants. FIG. 31 is a side elevation view of a ramp distraction spacer250, the opposite side being identical in appearance. The spacer 250 hasa main body portion 252 with a leading end 253. The ramp surface 254 ofspacer 250 is shown in FIG. 31. In transverse cross section, the regionof the main body 252 and leading end 253 between the ramp surfaces 254can be arcuate. It will be appreciated that ramp surface(s) 254 includesknurls 255 to reduce the chance of undesired movement followingplacement of distraction spacer 250 into a disk space.

FIG. 32 is a right side elevation of the distraction spacer 250 rotated90° around longitudinal axis X'--X' from the view in FIG. 31. Theopposite side of the view of FIG. 32 is identical in appearance. A frontview of the tapered surface 256 of the leading end 253 is shown in FIG.32. The relationship of the ramp surfaces 254 and the tapered surfaces256 at the leading end 253 is illustrated in FIG. 33. It will beappreciated that the leading end tip 257 need not be circular but can,for example, be oval in shape.

The ramp surfaces 254 of the distraction spacer 250 are symmetricallyopposed about the longitudinal axis X'--X' and form a ramp angle of γ.The angle γ and leading end tip 257 size are selected to permit ease ofinsertion of the distraction spacer 250 into the disk space. Thedistraction spacer is sized to have a main body 252 outer diameter D_(O)substantially equal to the midline disk height of a healthy disk in thepatient being treated. The axial length L' of the distraction spacer 250is approximate to the length L of the implant and sized for thedistraction spacer 250 to be fully inserted into the disk space withoutprotruding beyond the vertebrae.

Leading end 253 can also include a bore 260 which passes throughopposing tapered surfaces 256. The bore 260 provides for insertion ofpin 351 of T-device 350 illustrated in FIG. 37. T-device 350 canfacilitate removal of the spacer 250 from, for example, tool 300illustrated in FIG. 7A. The T-device 350 also includes a handle 352 forgrasping the device.

Near the trailing end 270, the distraction spacer 250 includes anannular groove 261 to permit a surgeon to grasp the distraction spacerif needed. The trailing end 270 is provided with an internally threadedaxial bore 272 for attachment of a placement tool 300.

FIG. 34 is a side elevation view of another embodiment of a rampdistraction spacer 500, the opposite side being identical in appearance.The spacer 500 has a main body portion 501 with a leading end 502. FIG.35 is a side elevation view of the distraction spacer 500 rotated 90°around longitudinal axis X'--X' from the view in FIG. 34, the oppositeside of the view being identical in appearance. FIG. 35 illustrates theramp surface 503 of spacer 500 including knurls 510. It will beappreciated that the embodiment of distraction spacer 500 does notinclude the annular groove 261 present in distraction spacer 250 (seeFIGS. 31-33).

The relationship of the tapered surface 504 of leading end 502 and rampsurfaces 503 are illustrated in the front end view of FIG. 36. A bore505 may also be present for operation of T-device 350. The leading endtip 508 of the illustrated embodiment of implant 500 is circular.

As discussed above, a kit containing numerous sized implants can beprovided with numerous sized distraction spacers having various rampangles.

With the invention as described, implants may maintain or increaselordosis. Further, the present invention permits formation of a tappedhole while removing debris which would otherwise obstruct implantinsertion. With the present invention, precise identity of depth ofinsertion of an implant on the left and the right side need not beattained, permitting greater versatility and tolerance of the method ofthe present invention to inaccuracies.

Having disclosed the invention in a preferred embodiment, modificationsand equivalents of the disclosed concepts may occur to one skilled inthe art. It is intended that the scope of the present invention not belimited to the specific embodiments disclosed, but shall include suchmodifications and equivalents.

What is claimed is:
 1. A kit for placing an implant into a disk spacebetween opposing vertebrae having opposing end plates to be separated bya predetermined degree of lordosis, said kit comprising:(A) an implanthaving:a generally frusto-conical hollow body having:a leading end atrailing end comprising:a trailing end rise a terminal end alongitudinal axis a first taper increasing from said leading end to saidtrailing end rise; and a second taper increasing from said terminal endto said terminal end rise said first taper of said frusto-conical bodyhaving a conical angle approximating said degree of lordosis; an implantthread pattern surrounding said body; openings formed through a conicalwall of said body into an interior of said body with said openingsformed at least on diametrically opposite sides of said body; saidimplant thread having a generally flat radial extremity in a surface ofa cone defined by said implant thread; (B) a tap having;a shaft defininga longitudinal axis; a tapping head at a distal end of said shaft, saidtapping head having a tapping thread surrounding said axis with a threadpattern substantially matching said implant thread pattern; said tappingthread includes a plurality of peaks and valleys defining a conical patharound said axis with a leading end tap diameter adjacent said distalend and with a trailing end tap diameter spaced from said distal end,said trailing end tap diameter being greater than said leading end tapdiameter; said leading end tap diameter being substantially equal tosaid leading end implant diameter.
 2. A kit according to claim 1whereinsaid tapping head includes a hollow body defining a tap interior;a plurality of channels for directing tapped debris from said tappingthread into said tap interior.
 3. A kit according to claim 2 whereinsaid tapping thread includes a plurality of axially extending groovesthrough said thread, said channels formed through said grooves and intosaid interior.
 4. A kit according to claim 2 wherein said channels areformed through said valleys.
 5. A kit according to claim 2 wherein anaxial end of said interior is closed at said distal end.
 6. A kitaccording to claim 1 wherein said tapping thread has a sharp radialextremity.
 7. A kit according to claim 1 further comprising adistraction spacer having:a rigid spacer body; said body having at leastdiametrically opposite exterior surfaces defining an angle substantiallyequal to said degree of lordosis.
 8. A kit for placing an implant into adisk space between opposing vertebrae having opposing end plates to beseparated by a predetermined degree of lordosis, said kit comprising:(A)an implant having;a generally frusto-conical hollow body having:aleading end a trailing end comprising:a trailing end rise a terminal enda longitudinal axis a first taper increasing from said leading end tosaid trailing end rise; and a second taper increasing from said terminalend to said terminal end rise; said first taper of said frusto-conicalbody having a conical angle approximating said degree of lordosis; animplant thread pattern surrounding said body; openings formed through aconical wall of said body into an interior of said body with saidopenings formed at least on diametrically opposite sides of said body;said implant thread having a generally flat radial extremity in asurface of a cone defined by said implant thread; said implant threadhaving a generally flat radial extremity in a surface of a cone definedby said implant thread; (B) a tap having:a shaft defining a longitudinalaxis; a tapping head at a distal end of said shaft, said tapping headhaving a tapping thread surrounding said axis with a thread patternsubstantially matching said implant thread pattern; said tapping threadincludes a plurality of peaks and valleys defining a conical path aroundsaid axis with a leading end tap diameter adjacent said distal end andwith a trailing end tap diameter spaced from said distal end, saidtailing end tap diameter being greater than said leading end tapdiameter; said leading end tap diameter being substantially equal tosaid leading end implant diameter; and said tapping thread having asharp radial extremity.
 9. A kit according to claim 8 wherein saidtapping head includes a hollow body defining a tap interior; a pluralityof channels for directing tapped debris from said tapping thread intosaid tap interior.
 10. A kit according to claim 9 wherein said tappingthread includes a plurality of axially extending grooves through saidthread, said channels formed through said grooves and into saidinterior.
 11. A kit according to claim 9 wherein said channels areformed through said valleys.
 12. A kit according to claim 9 wherein anaxial end of said interior is closed at said distal end.
 13. A kitaccording to claim 9 further comprising a distraction spacer having:arigid spacer body; said body having at least diametrically oppositeexterior surfaces defining an angle substantially equal to said degreeof lordosis.